This invention relates to an electrostatic printer and in particular to a non-impact printer using an OFT-tube.
In an electrostatic printer, a device for transmitting a light image to a photosensitive body or a photoreceptor to form an electrostatic image is generally called an "OFT-tube" or an "OFT-unit". The OFT-tube comprises a cathode ray tube and an about 5 mm-thick optical fiber plate or head plate which is comprised of a bundle of glass fibers normally having a diameter of about 20 .mu.m and joined to the surface of the cathode ray tube. The head plate of the OFT-tube is located a slight distance of 0.1 to 0.2 mm away from the surface of the photosensitive surface and a slight static electricity is formed on the head plate, causing the surface of the head plate to be contaminated by the deposition of a toner thereon and thus being unable to obtain a clean-cut image.
Japanese patent Disclosure No. 49-125038 (disclosed on Nov. 29, 1974-inventor: Tsukada et al) discloses an apparatus in which in order to prevent the surface of a head plate of an OFT-tube from being contaminated by a toner a transparent film is provided between the surface of a photosensitive body and the head plate so as to be moved relative to the photosensitive body and a cleaning liquid is supplied between the film and the photosensitive body to permit a proper voltage to be applied to the liquid. Since in this apparatus the cleaning liquid is flowed between the photosensitive body and the transparent film the setting position of the OFT-tube is restricted to a greater extent. Further, it is necessary to use a photosensitive body of greater size of diameter. In consequence, it would be difficult to provide a compact apparatus. The apparatus also requires a cleaning liquid supply means, a cleaning liquid collecting means and a means for applying a voltage to the cleaning liquid. As a result, the apparatus is complicated in its arrangement and it is not easy to exchange transparent films.